The present invention relates to flexible optoelectronic circuits, and, more particularly, to flexible optoelectronic circuits monolithically formed on a substrate and subsequently released from the substrate.
Flexible circuits, or three-dimensional circuits, have become more common as industrial and consumer electronics devices have become smaller and more portable. Flexible circuits are most commonly used in board-to-board, board-to-chip, and chip-to-chip connections in packages having limited space and stacked rigid boards, thus requiring three-dimensional connections. Some consumer applications include laptop computers, mobile phones, personal digital assistants, etc. Additionally, flexible circuits are increasingly used in mechanical devices requiring a mechanically dynamic circuit that permits motion, such as along robotic arms, fold areas, hinges, etc.
Flexible circuits began as a smaller alternative to ribbon cables and consisted of conducting elements providing interconnect of electronic assemblies. As the art progressed, circuit elements were fabricated from the electrical conductors. As optical componentry developed, manufacturers were pressed to add optical fibers to flexible circuits. These optical fibers could generally be arranged in special geometric orientations and mechanically manipulated to create passive optical circuit components as well, such as couplers, splitters, filters, etc.
Flexible circuits are generally formed from adhesively bonded laminates of dielectric. Dielectrics are laid out on a board and electrical conductors are plated using printed circuit board technology. Other flexible circuit fabrication techniques incorporate roll-to-roll processing.
Flexible circuits that incorporate optical and electrical components have become increasingly necessary, as the field of optoelectronics has spread into more and more applications. Generally, flexible circuits incorporating optical components are assembled with prefabricated optical fibers. These techniques require fabrication methods based on lamination of optical fibers between plies of flexible polyimide films. The flexible films add structural support so that the multiple fibers may be held in a curved or smoothly bent position, but do not enhance the performance of the fiber.
Increased use in progressive technology is primarily limited by size and density. Current technology of printed circuit board processing of flexible circuits provides that electronic and optical features are limited to features greater than about 250 xcexcm, which make higher density applications difficult.
Therefore, a need exists for development of optoelectronic flexible circuits to be implemented in high density and high frequency application relating to three-dimensional packaging of industrial and consumer electronics devices. The desired flexible optoelectronic circuit should be able to be manufactured from existing manufacturing techniques to avoid additional equipment and industrial cost to effectively and efficiently manufacture flexible circuits.
The present invention provides a multilayer flexible optoelectronic circuit that provides smaller density of optical elements within a flexible circuit. Additionally, an associated method for forming an optoelectronic circuit is provided.
A flexible optoelectronic circuit according to the present invention includes a first flexible insulating layer and an optical element deposited on a portion of the first insulating layer. Multiple optical elements may be provided. A second flexible insulating layer is deposited over the first insulating layer and optical element. The flexible optoelectronic circuit is formed on and subsequently released from a substrate and, therefore, independent of a substrate.
Additional embodiments of the flexible optoelectronic circuit include electrically conducting elements deposited within the circuit. For example, an electrical contact deposited within the first insulating layer is provided. A conductive layer is also provided and is deposited on the first flexible insulating layer and in electrical connectivity with the electrical contact. Additional embodiments include multiple conductive layers, separated by insulating layers. Similarly, multiple optical elements in additional layers including optical elements are also provided.
In one advantageous embodiment, the optical element deposited on a portion of an insulating layer comprises a first material and the first and second insulating layers comprise a second material. The first material has a higher refractive index than the second material thus permitting internal optical reflection and providing a waveguide. In one such embodiment, the optical element is integrally formed between first and second insulating layers by depositing compatible first and second materials in order to define the relationship of refractive indices thereto. Some such materials for accomplishing this include transparent organic materials comprising the first material, and photoimagable organic material comprising the second material. Examples of these organic materials include many polymers including polyimides, benzoncyclobutene, and polyfluorinatedcyclobutene.
Another advantageous embodiment of a flexible optoelectronic circuit includes a first flexible insulating layer and a second flexible insulating layer deposited on the first insulating layer. Defined on the second insulating is an optical element pattern. An optical element, as described above, is deposited within the optical pattern. Additional optical element patterns and optical elements are also provided according to some embodiments of the invention. A third flexible insulating layer deposited on the second insulating layer and the optical element. As such, the optoelectronic circuit is independent of a substrate, as described in the above embodiments. Conductive elements deposited between the insulating layers and, if desired, additional insulating layers are provide in other embodiments and constructed of materials as described above. Several embodiments include additional layers of optical elements deposited within additional insulating layers.
Another advantageous embodiment of an optoelectronic circuit includes a substrate and a release layer deposited on the substrate upon which flexible insulating layers, including optical elements, are formed. According to this embodiment, a first flexible insulating layer deposited on the release layer and an optical element is deposited on a portion of the first insulating layer. A second flexible insulating layer is deposited on the first insulating layer and the optical element. As such, the first and second insulating layers comprise a flexible optoelectronic circuit when separated from the substrate and release layer.
According to one embodiment of the optoelectronic circuit the substrate is a semiconductor material. It is advantageous for the release layer to comprise an oxide layer formed on the semiconductor material. As such, the oxide layer permits the flexible optoelectronic circuit to be removed from the substrate using standard etching techniques.
Alternatively, the release layer may comprise an ultraviolet sensitive adhesive, which permits exposing to ultraviolet light to release to adhesive from the substrate. An additional embodiment of a flexible optoelectronic circuit according to the present invention comprises a first flexible insulating layer including an electrical contact deposited within. The electrical contact is in electrical connectivity with a first conductive layer deposited on the first insulating layer. A second flexible insulating layer is deposited on the first insulating layer and includes at least one optical element pattern defined therein. An optical element deposited within the optical pattern of the second insulating layer. A third flexible insulating layer is deposited on the second insulating layer and the optical element. As such, the optical element is formed of a material having an index of refraction higher than the indices of refraction of the material forming the flexible insulating layers. Also, according to this embodiment of the flexible optoelectronic circuit, the optoelectronic circuit is formed on and subsequently released from a substrate and, therefore, independent of a substrate.
Another aspect of the present invention includes a method of forming a flexible optoelectronic circuit. One embodiment of the method comprises depositing a release layer on a substrate, depositing a first and second flexible insulating layer first on the substrate. The method includes defining at least one optical element pattern in the second flexible layer, to permit depositing an optical element within the optical element pattern. Additionally, the method includes depositing a third flexible insulating layer on the second flexible insulating layer and the optical element. Upon completing the construction foregoing construction steps the release layer is released from the first flexible insulating layer in order to remove the substrate from the flexible optoelectronic circuit. The resultant product is a flexible optoelectronic circuit.
In one embodiment of the method for forming an optoelectronic circuit, the step of depositing a release layer comprises depositing an oxide layer on a semiconductor substrate. Alternatively, the step of depositing an oxide layer may comprise growing an oxide layer on the semiconductor substrate. One embodiment of releasing the release layer may then comprise etching the oxide layer from the substrate.
Other embodiments of the method of forming a flexible optoelectronic circuit include applying common monolithic manufacturing methods. For example, on embodiment includes depositing the first, second, and third insulating layers comprises depositing via spin-on deposition. Other methods include depositing insulating layers comprising photoimagable organic material and imaging the photoimagable organic material in order to define optical patterns in an insulating layer. Additionally, depositing transparent organic material in the defined optical patterns is also provided according to one embodiment of the method. As such, depositing the transparent organic material includes depositing a material with a higher index of refraction the material deposited to form the insulating layers. Some types of material comprising the photoimagable organic material and transparent organic material include polyimides, benzocyclobutene, and polyfluorinatedcyclobutene.
One advantageous embodiment of the method for forming a flexible optoelectronic circuit additionally comprises depositing a conductive layer on at least one of the described insulating layers. These embodiments may include depositing electrical contacts within the first insulating layer, wherein the electrical contacts are in electrical connectivity with the conductive layer.
Yet another embodiment of forming a flexible optoelectronic circuit is provided. This embodiment comprises depositing a release layer on a substrate, and subsequently depositing first and second flexible insulating layers on the substrate and release layer. An optical element is deposited on a portion of the first flexible insulating layer between the first and second insulating layers. Upon completing the construct of the flexible circuit, the method includes releasing the release layer so as to remove the release layer and the substrate. Thus a flexible optoelectronic circuit is provided from the method. The present invention also includes the optical electronic circuit provided by the method described herein.